TABLE 42 Data from Table 38 in This Report on All Relevant Ductile Iron Pipe with Polyethylene Encasement and Cathodic Protection in Corrosive Soils
Abbreviated Project Name 
Total Project Age, t_{i} (years) 
Average Age (years) 
Length, l_{i} (miles) 
t_{i} × l_{i} 
Failures 
Failure Rate (failures/mile/year) 
WEB 
24 
12 
150 
3,600 
0 
0 
Southwest 
25 
20.5 
75.8 
1,895 
1 
0.000528 
MidDakota 
12 
9 
49.6 
595.2 
0 
0 
Montrose 
27 
27 
27 
729 
0 
0 
Hanna 
20 
20 
7 
140 
0 
0 
Santa Margarita 
23 
23 
7.5 
172.5 
0 
0 
Vacaville 
24 
24 
3 
72 
0 
0 
Akron 
7 
7 
0.25 
1.75 
1 
0.571429 
Trinidad 
29 
27.5 
10 
290 
0 
0 
California City 
25 
16.5 
1.5 
37.5 
1 
0.026667 
Denver 
24 
24 
9 
216 
0 
0 
Sheridan 
16 
15 
12 
192 
0 
0 
TOTALS 


352.65 
7,940.95 


SOURCE: In Chapter 3 of this report, see Table 38, “Partial List of Cathodically Protected PolyethyleneEncased Ductile Iron Pipelines.” 
year. This threshold value is only slightly lower than that provided by Reclamation (Threshold 1).
The thresholds estimated in the previous subsections can be used to calculate the probability of having no failures over a 50year period. Also, the data can be used to estimate the probability of having one or more failures. Assuming that the annual probability of failure per mile remains constant over time^{10} and that each year is statistically independent, the probability of having zero failures over a 50year period for a given mile of pipe can be determined as follows:
Using the threshold values determined in the previous subsections and Equation 43, the probability of having no failures for a given mile of pipe over a 50year period for each threshold value is shown in Table 43, and the trend in the probability with threshold is linear, as shown in Figure 42. The probability of